Instrumental function of the SPECS XPS system

A simple method for the energy resolution measurement of a spectrometer, working in the fixed analyser transmission mode, is proposed and used to determine the resolution of a SPECS Phoibos 100 spectrometer, being a part of an X-ray Photoelectron Spectroscopy (XPS) setup. The spectrometer resolution was obtained from the O 1s photoelectron line profiles, taken from the oxidized boron-doped silicon single crystal vs. the analyzer pass energy. The measurements were performed for two entrance slits having respective widths of 1 mm and 7 mm. An excellent agreement with the theoretical expectations was obtained for the narrower slit, showing linear dependence on the pass energy. As for the wider slit, agreement with theory is achieved only for lower pass energies. At higher pass energies, the resolution shows non-linear behaviour and even saturation, while the analyzer transmission continues to grow. The instrumental function of the whole XPS system is determined as a convolution of the spectrometer instrumental function and the X-ray energy profile. The usefulness of the total instrumental function for the analysis of valence band spectra was also tested. For that purpose, a novel deconvolution procedure is introduced, giving a possibility to analytically calculate the position of the valence band maximum, providing excellent agreement in the case of high resolution spectra. When the valence band spectra are taken in lower resolution, deconvolution efficiently reduces the spectrum deviations due to the lower resolution, although the valence band maximum determination is less precise.